Affiliation:
1. Faculty of Chemistry and Food Chemistry Technische Universität Dresden 01062 Dresden Germany
2. Institute of Inorganic Chemistry Universität Regensburg 93040 Regensburg Germany
3. Wilhelm Ostwald Institute for Physical and Theoretical Chemistry Universität Leipzig 04103 Leipzig Germany
4. Department of Chemistry and Polymer Science Stellenbosch University Stellenbosch 7602 South Africa
Abstract
AbstractAlthough diphosphene transition metal complexes are known to undergo E to Z isomerization upon irradiation with UV light, their potential for photoswitching has remained poorly explored. In this study, we present diphosphene complexes capable of reversible photoisomerizations through haptotropic rearrangements. The compounds [(2‐κ2P,κ6C)Mo(CO)2][OTf] (3 a[OTf]), [(2‐κ2P,κ6C)Fe(CO)][OTf] (3 b[OTf]), and [(2‐κ2P)Fe(CO)4][OTf] (4[OTf]) were prepared using the triflate salt [(LC)P=P(Dipp)][OTf] (2[OTf) as a precursor (LC=4,5‐dichloro‐1,3‐bis(2,6‐diisiopropylphenyl)‐imidazolin‐2‐yl; Dipp=2,6‐diisiopropylphenyl, OTf=triflate). Upon exposure to blue or UV light (λ=400 nm, 470 nm), the initially red‐colored η2‐diphosphene complexes 3 a,b[OTf] readily undergo isomerization to form blue‐colored η1‐complexes [(2‐κ1P,κ6C)M(CO)n][OTf] (5 a,b[OTf]; a: M=Mo, n=2; b: M=Fe, n=1). This haptotropic rearrangement is reversible, and the (κ2P,κ6C)‐coordination mode gradually reverts back upon dissolution in coordinating solvents or more rapidly upon exposure to yellow or red irradiation (λ=590 nm, 630 nm). The electronic reasons for the reversible visible‐light‐induced photoswitching observed for 3 a,b[OTf] are elucidated by DFT calculations. These calculations indicate that the photochromic isomerization originates from the S1 excited state and proceeds through a conical intersection.